Demand for magnesium (Mg) metal is increasing rapidly due to uses in lightweight high strength alloys for automobiles, aerospace, and building construction. However, worldwide supply is flat or declining. Seawater represents a virtually unlimited source of Mg that could supply worldwide demand if an economically and environmentally sound method were available for its extraction. Mg is commonly obtained from the high temperature Pidgeon process in which a Mg-bearing mineral such as dolomite is reacted with FeSi. Mg is also obtained by electrolysis of MgCl2 salts recovered from seawater or other brine sources such as the Great Salt Lake (UT, USA). However, conventional electrolysis of molten salts requires high purity (94% or better) MgCl2 salts. High-purity MgCl2 salts are presently obtained through a complex series of steps including precipitation, solvent extraction, water evaporation, dehydration of MgCl2.nH2O salts, and high-temperature carbothermic reduction of impure salts recovered as evaporates from spray-dried brines. However, water evaporation from MgCl2 brines and dehydration of MgCl2.nH2O salts prior to MgCl2 electrolysis are energy intensive steps. The only remaining commercial operation in the U.S. for production of Mg metal (U.S. Magnesium, LLC, Salt Lake City, Utah, USA) produces Mg from water taken from the Great Salt Lake (Utah, USA). This high-temperature plant requires 44 kWh/kg of energy at a production cost of $3.31/kg. However, in its Modern Electro/Thermochemical Advances In Light Metal Systems (METALS) program, the Advanced Research Projects Agency-Energy (ABPA-E) set ambitious target goals for both energy (27 kWh/kg) and cost of production ($2/kg). Accordingly, new processes are needed that produce Mg at these much lower energy and production costs in addition to dramatically lowering peak process temperatures (<350° C.). The present invention addresses these needs.